Objective: Marijuana (MJ) use is associated with adverse effects on fetal growth. We aimed to investigate the timing of suboptimal fetal growth onset in MJ-exposed pregnancies. In addition, we aimed to explore the relationship between MJ-exposure and both abnormal uterine artery (UtA) Doppler parameters and small for gestational age (SGA).
Study design: This was a secondary analysis of a prospective multicenter cohort that enrolled nulliparous individuals delivering non-anomalous fetuses beyond 20 weeks' gestation. Marijuana exposure was ascertained by self-report or clinical urine toxicology testing. Ultrasound estimated fetal weights (EFWs) were assessed in participants at both 16w0d-21w6d and 22w0d-29w6d. EFWs and birth weight (BW) were converted to weight percentiles (wPCT). EFW and BW wPCTs were calculated using population-based standards. Additionally, a customized standard designed to be applicable to both EFWs and BWs within the same model was also used to allow for EFW to BW percentile trajectories. The primary outcome, longitudinal wPCT, was compared between individuals with and without MJ use in a linear mixed-effects regression model adjusting for tobacco. For modeling, wPCT was smoothed across gestational age; MJ was estimated as an intercept and linear difference in the slope of gestational age. UtA Doppler notching, resistance index (RI), and pulsatility index (PI) at 16w0d-21w6d were compared using t-test and χ2. SGA at delivery was also compared.
Results: Nine thousand one hundred and sixty-three individuals met inclusion criteria; 136 (1.5%) used MJ during pregnancy. Individuals who used MJ were more likely to be younger, identify as non-Hispanic Black, and have had less education. Fetuses exposed to MJ had lower wPCT beginning at 28 weeks using population-based and customized standards, when compared to those without exposure. UtA notching, PI, and RI were similar between groups. SGA was more frequent in neonates exposed to MJ using both population-based (22 vs. 9%, p<.001) and customized (25 vs. 14%, p<.001) curves.
Conclusions: MJ-exposed fetuses were estimated to be smaller than unexposed fetuses starting at 28 weeks' gestation across both growth standards without a difference in UtA Doppler parameters.
Keywords: Marijuana; birth weight; fetal growth; uterine artery Doppler; weight percentile.